Magnetoresistive device and method for manufacturing the same

ABSTRACT

A magnetoresistive device includes a carrier, an xMR-sensor, a magnetic layer formed above an active xMR-region of the xMR-sensor and an insulating layer arranged between the xMR-sensor and the magnetic layer.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.13/019,510 filed on Feb. 2, 2011, and incorporated herein by referencein its entirety.

FIELD

The invention is directed to a magnetoresistive device and a method formanufacturing the same. Further embodiments of the invention relate tomagnetoresistive sensors, which are based on xMR technology, that may beemployed in rotational speed sensor applications.

BACKGROUND

Today, speed sensors based on magnetoresistive devices including xMRstructures are commonly used for rotational speed sensor applications.Such xMR based speed sensors are employed, for example, with a magneticpole wheel as a transducer wheel. The magnetoresistive devices based onxMR technology may include xMR structures such as anisotropicmagnetoresistance (AMR) structures, giant magnetoresistance (GMR)structures, or tunnel magnetoresistance (TMR) structures.

SUMMARY

Embodiments of the invention provide a magnetoresistive device,comprising a carrier, and an xMR-sensor situated on the carrier. Thedevice further comprises a magnetic layer formed above an activexMR-region of the xMR-sensor, and an insulating layer arranged betweenthe xMR-sensor and the magnetic layer.

Embodiments of the invention provide a magnetoresistive device,comprising a carrier, an xMR-sensor situated on the carrier that isbased on an anisotropic magnetoresistance (AMR) effect, a giantmagnetoresistance (GMR) effect, or a tunnel magnetoresistance (TMR)effect. The device further comprises a hard magnetic layer formed abovean active xMR-region of the xMR-sensor, and an insulating layer arrangedbetween the xMR-sensor and the hard magnetic layer. The hard magneticlayer is configured to provide a bias magnetic field for the activexMR-region of the xMR-sensor from above, and a vertical distance betweenthe xMR-sensor and the hard magnetic layer is smaller than a lateraldimension of the hard magnetic layer.

Embodiments of the invention provide a magnetoresistive device,comprising an xMR-sensor, and means for providing a bias magnetic fieldfor an active xMR-region of the xMR-sensor from a position above thexMR-sensor.

Embodiments of the invention provide a method for manufacturing amagnetoresistive device. The method comprises providing an xMR-sensor,and forming a magnetic layer above an active xMR-region of thexMR-sensor. In one embodiment, the xMR-sensor and the magnetic layer areintegrated together to form an integrated circuit type device.

Embodiments of the invention provide a method for manufacturing amagnetoresistive device. The method comprises providing an xMR-sensorbased on an anisotropic magnetoresistance (AMR) effect, a giantmagnetoresistance (GMR) effect, or a tunnel magnetoresistance (TMR)effect, and forming a hard magnetic layer above an active xMR-region ofthe xMR-sensor. In addition, the method comprises arranging aninsulating layer between the xMR-sensor and the hard magnetic layer,wherein the step of arranging the insulating layer is performed beforethe step of forming the hard magnetic layer above the active xMR-regionof the xMR-sensor.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a schematic cross-sectional view of a magnetoresistivedevice according to an embodiment of the present invention;

FIG. 2 shows a graph of an example magnetic field intensity generated atthe location of an xMR-sensor of the embodiment of the magnetoresistivedevice in accordance with FIG. 1;

FIG. 3 a shows a schematic cross-sectional view of an embodiment of anxMR-wafer present after an FE-(Front-End) process and grinding;

FIG. 3 b shows a schematic top view of the embodiment of the xMR-waferin accordance with FIG. 3 a;

FIG. 4 a shows a schematic cross-sectional view of an embodiment of amanufacturing part of a magnetoresistive device after reconstitution;

FIG. 4 b shows a schematic top view of the embodiment of themanufacturing part of the magnetoresistive device in accordance withFIG. 4 a;

FIG. 5 a shows a schematic cross-sectional view of an embodiment of amanufacturing part of a magnetoresistive device after deposition of afirst dielectric layer;

FIG. 5 b shows a schematic top view of the embodiment of themanufacturing part of the magnetoresistive device in accordance withFIG. 5 a;

FIG. 6 a shows a schematic cross-sectional view of an embodiment of amanufacturing part of a magnetoresistive device after deposition andpatterning of a hard magnetic material;

FIG. 6 b shows a schematic top view of the embodiment of themanufacturing part of the magnetoresistive device in accordance withFIG. 6 a;

FIG. 7 a shows a schematic cross-sectional view of an embodiment of amanufacturing part of a magnetoresistive device after patterning of aredistribution metal, deposition of a final dielectric layer and anopening;

FIG. 7 b shows a schematic top view of the embodiment of themanufacturing part of the magnetoresistive device in accordance withFIG. 7 a;

FIG. 8 a shows a view on a Bx/Bz plane of a schematic setup of anembodiment of an xMR speed sensor in a pole wheel configuration;

FIG. 8 b shows a view on a By/Bz plane of the embodiment of the xMRspeed sensor in accordance with FIG. 8 a;

FIG. 9 shows a schematic illustration of a magnetic field rotationacross an xMR stripe length when a stripe is positioned in the center ofthe pole wheel depicted in FIG. 8 a;

FIG. 10 shows a graph of a simulated xMR response upon rotation of arotating magnetic field, illustrating a characteristic discontinuity;

FIG. 11 a shows a bird's view on simulated magnetization regions of thefree layer of an xMR stripe for a magnetic field angle of 5°corresponding to point 1 in FIG. 10;

FIG. 11 b shows a bird's view on simulated magnetization regions of thefree layer of an xMR stripe for a magnetic field angle of 45°corresponding to point 2 in FIG. 10; and

FIG. 11 c shows a bird's view on simulated magnetization regions of thefree layer of an xMR stripe for a magnetic field angle of 60°corresponding to point 3 in FIG. 10.

DETAILED DESCRIPTION

Many of today's xMR based speed sensors are employed with a magneticpole wheel as a transducer wheel.

The xMR structures are usually narrow stripes with a homogeneous widthof <2 μm in order to provide a defined sensitivity by the shapeanisotropy. To achieve a reasonable xMR resistance in the range of 10kOhms, the stripe is several 100 μm long. The transducer pole wheelshave only a limited thickness/axial width and therefore, the magneticsignal field is not homogeneous over the whole stripe length. Withgrowing (axial) distance from the pole wheel center, the By componentincreases and is phase shifted by 180° between the lower and upper halfof the pole wheel (see, e.g., FIGS. 8 a,8 b and 9). In combination witha Bx component which is phase shifted by +/−90° to the individual Bycomponents, this results in a rotation of the magnetic field vector.

The shape anisotropy results in a different behavior of themagnetizations over the stripe width: whereas the domains in the centercan follow quite easily an external magnetic field, the magnetizationregions at the edges are much more stable. FIGS. 11 a,11 b, and 11 cshow a bird's eye view on the simulated magnetization of the free layer(i.e. sensor layer) of the xMR stack upon exposure to an externalrotating field with Bx=By=8 mT. The rotation starts at phi=0° with themagnetic field pointing to the right. At phi=5° (point 1 in FIG. 10) thecenter magnetization region can follow whereas the edge regions keeptheir magnetization in the initial direction in the upper half space. Afurther clockwise rotation (phi=45° corresponding to point 2 in FIG. 10)leads to a generation of 180° domain walls between the magnetizations ofthe stripe center and the edge. At around phi=60° rotation angle(corresponding to point 3 in FIG. 10) the force on the edge regions isstrong enough to turn their magnetization direction along the externalfield. This switching process is reflected in a discontinuity in theresistance characteristic (see FIG. 10). FIG. 10 shows an example graphof a simulated xMR response upon exposure to a rotating magnetic field(B=8 mT). Referring to FIG. 10, a discontinuity in the characteristiccan be observed between field angles of 55° and 60°. The field anglewhere the switching occurs depends on the field conditions (By/Bx ratio)of the rotating field vector and the shape anisotropy and therefore, thestripe width.

The discontinuity in the output signal can heavily affect theinterpretation of the signal (jitter, pulse lost, etc.)

According to the prior art, methods for creating a uni-axial biasmagnetic field for stabilizing the direction of free layer magnetizationexist. By using such a bias field, discontinuities in the output signalgenerated by rotating free layer magnetization can be prevented or atleast reduced. Known methods to create such a bias field employ, forexample, the use of a hard magnetic bias material at the edges of thesensor layer, the exchange biasing of the free layer with a naturalantiferromagnet, or the mounting of a bias magnet to the back of thesensor.

In particular, the use of a hard magnetic bias material at the edges ofthe sensor layer can be used only for very short devices, while theexchange biasing of the free layer with a natural antiferromagnettypically creates a rather large bias field. In addition, the method ofmounting a bias magnet to the back of the sensor is rather complex andincreases the cost of manufacturing the device and increases its size.

Therefore, a need exists for an improved concept of a magnetoresistivedevice, which, on the one hand, allows for a compact and flexiblestructure and, on the other hand, allows for a less complex andcost-effective manufacturing of the same.

Embodiments of the invention provide a compact and flexible structurethat can be achieved if a magnetic layer is formed above an activexMR-region of the xMR-sensor. By this measure, disadvantages in terms ofcomplexity, cost and size may be overcome, thereby realizing an improvedconcept of a compact and flexible magnetoresistive device.

FIG. 1 shows a schematic cross-sectional view of a magnetoresistivedevice 100 according to an embodiment of the present invention. As shownin FIG. 1, the magnetoresistive device 100 comprises a carrier 110, anxMR-sensor 120, a magnetic layer 130 and an insulating layer 140. Here,the magnetic layer 130 is formed above an active xMR-region of thexMR-sensor 120. In addition, the insulating layer 140 is arrangedbetween the xMR-sensor 120 and the magnetic layer 130.

The xMR-sensor 120 of the magnetoresistive device 100 can, for example,be based on an anisotropic magnetoresistance (AMR) effect, a giantmagnetoresistance (GMR) effect, or a tunnel magnetoresistance (TMR)effect. It can be seen in FIG. 1 that the magnetoresistive device 100may also comprise two or more xMR-sensors which are arranged next toeach other on the carrier 110. The two or more xMR-sensors can be usedin one embodiment to detect a gradient of an externally applied magneticfield.

The carrier 110 of the magnetoresistive device 100 can, for example, bea semiconductor substrate made of silicon.

In the embodiment of FIG. 1, the magnetic layer 130 of themagnetoresistive device 100 is configured to provide a bias magneticfield for the active xMR-region of the xMR-sensor 120 from above. Thisessentially can be achieved by forming the magnetic layer 130 above theactive xMR-region of the xMR-sensor 120. The presented measure allowsfor an improved functionality of the magnetoresistive device andprovides an easier usage, handling and manufacturing of the same.

Thus, according to the embodiment of FIG. 1, the magnetic layer isconfigured to provide a bias magnetic field for the active xMR-region ofthe xMR-sensor from above.

According to embodiments of the present invention, the magnetic layer130 of the magnetoresistive device 100 may be configured as a hardmagnetic layer or a soft magnetic layer. The hard magnetic layer, forexample, can be made of a hard magnetic material comprising SmCo, hardferrite or NdFeB. The soft magnetic layer, for example, can be made of asoft magnetic material exchange biased by a natural antiferromagnet.

Referring to the embodiment of FIG. 1, the vertical distance d_(v)between the xMR-sensor 120 and the magnetic layer 130 lies within arange of approximately 1 to 100 μm, preferably 3 to 10 μm. Because ofthis small vertical distance, the bias magnetic field provided by themagnetic layer 130 can be generated in direct vicinity to the xMR-sensor120 of the magnetoresistive device 100.

According to further embodiments, the magnetic layer 130 is configuredas a hard magnetic layer having a magnetization direction along thedirection of the easy axis of the xMR-sensor 120. In this way, it can beinsured that a bias magnetic field will be generated from the hardmagnetic layer in the active xMR-region of the xMR-sensor 120 along theeasy axis of the xMR-sensor 120.

In particular, the hard magnetic layer 130 can be provided with amagnetization, a thickness and a vertical distance d_(v) from thexMR-sensor 120 such that a strength of the bias magnetic field generatedalong the easy axis of the xMR-sensor 120 will be between approximately2 and 10 mT.

As a consequence, the strength of the bias magnetic field generatedalong the easy axis of the xMR-sensor can be variably adjusted, so thata rotating free layer magnetization in the active xMR-region of thexMR-sensor can be avoided or at least minimized, thereby reducingdiscontinuities in the output signal of the xMR-sensor. It is pointedout here that the bias magnetic field to be generated along the easyaxis of the xMR-sensor can be applied to stabilize the direction of thefree layer magnetization without having to increase the complexity, costand size of the magnetoresistive device.

FIG. 2 shows a graph of an example magnetic field intensity generated atthe location of an xMR-sensor of the embodiment of the magnetoresistivedevice in accordance with FIG. 1. In particular, three curves 210, 220,and 230 of the magnetic field intensity generated by a 1 μm thickSmCo-layer (hard magnetic layer) at various distances are shown in FIG.2. The vertical axis of the graph represents the magnetic fieldintensity (1 mT˜796 A/m), while the horizontal axis of the graphrepresents the position at a lateral direction or the x-direction at agiven distance from the SmCo-layer. Here, the 1 μm thick SmCo-layer maycorrespond to the magnetic layer 130 of the magnetoresistive device 100as shown in FIG. 1. The various distances associated with the differentcurves 210 220, and 230 in the graph of FIG. 2 may correspond todifferent vertical distances d_(v) (e.g., 1 μm, 10 μm and 100 μm,respectively) between the xMR-sensor 120 and the magnetic layer 130 ofthe magnetoresistive device 100. It can be seen clearly in FIG. 2 thatthe three curves 210, 220, and 230 of the magnetic field intensity arenearly identical within a range of approximately 0.2-0.8 mm, while theysignificantly deviate from each other outside of this range. It is to benoted that the magnetic field intensity is plotted with a logarithmicscale here. The characteristic behavior of the different curves 210,220, and 230 shows that the generated magnetic field intensity is notinfluenced substantially by variations in the distance between thexMR-sensor and the magnetic layer. Therefore, the magnetoresistivedevice can be made robust against such variations in the distance.

Thus, referring to FIG. 2, the simulation shows little influence in thefield intensity up to vertical distances d_(v) of 100 μm. In embodimentsof the present invention, the vertical distance d_(v) is betweenapproximately 1 to 100 μm, preferably between 3 to 10 μm.

According to further embodiments of the present invention, a method formanufacturing a magnetoresistive device may comprise the followingsteps. First, an xMR-sensor is provided. Then, a magnetic layer isformed above an active xMR-region of the xMR-sensor. Here, it is pointedout that the xMR-sensor may be provided on top of an CMOS circuitry inone embodiment, essentially representing an integrated sensor.

According to further embodiments, the method for manufacturing themagnetoresistive device may further comprise arranging an insulatinglayer between the xMR-sensor and the magnetic layer. Here, the step ofarranging the insulating layer is performed before the step of formingthe magnetic layer above the active xMR-region of the xMR-sensor.

Moreover, the magnetoresistive device obtained from the manufacturingprocess including the xMR-sensor, the magnetic layer and the insulatinglayer may correspond to the magnetoresistive device 100 including thexMR-sensor 120, the magnetic layer 130 and the insulating layer 140,respectively.

FIGS. 3 a, 3 b-7 a, 7 b show schematic cross-sectional views andcorresponding top views of embodiments of manufacturing parts of amagnetoresistive device obtained after different steps in themanufacturing process.

Referring to FIGS. 3 a, 3 b-7 a, 7 b, the procedure for manufacturingthe magnetoresistive device according to one embodiment of the presentinvention is briefly described in the following. Here, thecross-sectional views of FIGS. 3 a-7 a are taken along the lines A-A inFIGS. 3 b-7 b, while the top views of FIGS. 3 b-7 b shows the structuresof FIGS. 3 a-7 a adjacent to each other.

First, an xMR-wafer or GMR-wafer is processed through the FE (Front-End)in a standard way and then thinned down. Thinning down the xMR-wafer canbe achieved by a grinding process in one embodiment. As a startingpoint, the xMR-wafer after the FE-process and the grinding is obtained,is shown in FIG. 3 a or 3 b, respectively. In FIGS. 3 a and 3 b, thecarrier 110, such as an Si-chip including CMOS circuitry, and one ormore xMR-sensors 120, such as a GMR-sensor, are depicted. Moreover, anopening and a contact pad 150 may be provided onto or into the carrier110.

After this, in one embodiment the xMR-chips are singulated, placed on afoil and reconstituted to a wafer-like substrate using a mold compound.FIGS. 4 a and 4 b show the processing result after the reconstitution.In particular, a mold 160 is depicted in FIGS. 4 a and b surrounding thecarrier 110.

After removal of the foil, an insulating layer 140 or dielectric layeris deposited on top of the passivation layer or photoimide with athickness ranging between 3-10 μm. The processing result afterdeposition of the insulating layer 140 or the first dielectric layerwith a thickness of e.g. 5 μm is depicted in FIG. 5 a or 5 b,respectively. As can be seen in FIGS. 5 a and 5 b, the insulating layer140 covers the carrier 110 completely and extends within an area definedby an inner perimeter of the mold 160. In other words, the step ofarranging the insulating layer comprises depositing a dielectric layerhaving a thickness between 3 and 10 μm.

Subsequently, a magnetic layer 130 such as a hard magnetic layer made,e.g., of SmCo, NdFeB or hard ferrite is formed above the activexMR-region of the xMR-sensor 120 such that the field generated by thislayer 130 at the location of the xMR-sensors 120 or xMR-elements isalong the easy axis of the xMR-sensors or xMR-elements and has astrength of between 2 mT and 10 mT. This, for example, can be achievedby an SmCo layer with a thickness of approximately 3 μm. The processingresult of a deposition and patterning of a hard magnetic material (e.g.a 3 μm thick hard magnetic SmCo-layer) is depicted in FIGS. 6 a and 6 b,respectively. It can be seen from FIGS. 6 a and 6 b that the magneticlayer 130 is formed above an active xMR-region of the xMR-sensor 120,wherein a vertical distance d_(v) between the xMR-sensor 120 and themagnetic layer 130 is smaller than a lateral dimension d_(l) of themagnetic layer 130. As has been described with reference to FIG. 2, anadvantage of such a configuration is that variations in the distancebetween the xMR-element and the hard magnetic layer have a negligibleeffect as long as the distance is small compared to the lateraldimension of the bias layer.

Thus, according to the embodiment described above, a vertical distancebetween the xMR-sensor and the magnetic layer is smaller than a lateraldimension of the magnetic layer. In this way, it is possible to avoid aninfluence of variations in the distance between the xMR-sensor and themagnetic layer on the performance reliability of the magnetoresistivedevice.

Following the formation of the magnetic layer 130 or bias layer, anotherdielectric layer, a redistribution metal layer and a final dielectriclayer (structure 170) are deposited. The processing result afterpatterning of the redistribution metal, deposition of a final dielectriclayer (third ILD, Inter-Layer Dielectric) and an opening is shown inFIG. 7 a or 7 b, respectively. Referring to FIGS. 7 a and 7 b, anopening in the final dielectric layer and a via 180 filled, for example,with a metallic material are provided, thereby realizing an electricalcontact with the pad 150.

The example process flow described with reference to FIGS. 3 a, 3 b-7 a,7 b can advantageously be used for manufacturing of a magnetoresistivedevice with a reduced process complexity, cost and size.

Embodiments of the present invention provide the advantage thatdiscontinuities in the output signal generated by a rotating free layermagnetization can be prevented or at least reduced. Moreover,disadvantages in terms of process complexity, cost and size of theresulting sensor device can be avoided.

Embodiments of the present invention provide a concept for creating auni-axial bias field along the easy axis of an xMR-sensor withoutsignificant costs added and without change of the final sensor device.

The present invention provides this concept by creating bias fields inthe extreme vicinity of the xMR-sensor elements after finishing thestandard wafer process of the integrated device. This vicinity can beachieved by employing a wafer level approach to create a magnetic layeror intermediate layer on the face side of the xMR-sensor, whichcontains, e.g. a thin hard magnetic material (electro-deposited orsputtered) or a soft magnetic layer, exchange biased by a naturalantiferromagnet.

An advantage of the method according to an embodiment of the presentinvention is that the magnetic layer or intermediate layer (bias layeror biasing layer) allows one to create a magnetic bias field in directvicinity to the sensor layer or free layer, thereby significantlyreducing the amount of material needed.

Embodiments of the present invention also provide the advantage that thebias field can be tuned easily by varying the thickness of the (biasing)layer. In addition, variations in the distance between biasing layer andsensor have negligible influence. In embodiments of the presentinvention, no modification of the sensor element itself is required, sothat no influence on the reliability of the device is to be expected.

The present invention provides a very cost-effective solution due to theapplication of semiconductor methodology. Embodiments of the presentinvention provide a design of a bias layer which easily can be changedvia lithography.

As opposed to the prior art, it has been found that no significantchanges to the integration process have to be made if the process isperformed in the presented way. Embodiments of the present inventionprovide an add-on process flow that can be performed withoutconsideration of the integration technology used for the sensor elementitself and, specifically, for integrated CMOS and xMR-sensors.

Embodiments of the invention are not restricted in flexibility andefficiency and are advantageous in terms of complexity, cost and size.

In summary, the present invention is realized by utilizing a wafer levelapproach to create a biasing layer in direct vicinity to thexMR-elements. This can, for example, be achieved by adding a dedicatedmetallization level on top of the xMR-sensor wafer or by utilizing aneWLB (embedded Wafer Level Ball Grid Array) approach.

Although some aspects have been described in the context of anapparatus, it is clear that these aspects also represent a descriptionof the corresponding method, where a block or device corresponds to amethod step or a feature of a method step. Analogously, aspectsdescribed in the context of a method step also represent a descriptionof a corresponding block or item or feature of a correspondingapparatus.

The above described embodiments are merely illustrative for theprinciples of the present invention. It is understood that modificationsand variations of the arrangements and the details described herein willbe apparent to others skilled in the art. It is the intent, therefore,to be limited only by the scope of the impending patent claims and notby the specific details presented by way of description and explanationof the embodiments herein.

1. A magnetoresistive device, comprising: a carrier; an xMR-sensorformed on or in the carrier; a magnetic layer distinct from thexMR-sensor and formed above an active xMR-region of the xMR-sensor; andan insulating layer distinct from the xMR-sensor and arranged betweenthe xMR-sensor and the magnetic layer.
 2. The magnetoresistive deviceaccording to claim 1, wherein the magnetic layer is configured toprovide a bias magnetic field for the active xMR-region of thexMR-sensor from a position above the xMR-sensor.
 3. The magnetoresitivedevice according to claim 1, wherein the magnetic layer comprises a hardmagnetic layer or a soft magnetic layer.
 4. The magnetoresistive deviceaccording to claim 1, wherein a vertical distance between the xMR-sensorand the magnetic layer is smaller than a lateral dimension of themagnetic layer.
 5. The magnetoresistive device according to claim 4,wherein the vertical distance between the xMR-sensor and the magneticlayer lies within a range of 1 μm to 100 μm.
 6. The magnetoresistivedevice according to claim 1, wherein the xMR-sensor is based on ananisotropic magnetoresistance (AMR) effect, a giant magnetoresistance(GMR) effect, or a tunnel magnetoresistance (TMR) effect.
 7. Themagnetoresistive device according to claim 1, wherein the magnetic layercomprises a hard magnetic layer, and wherein the hard magnetic layercomprises a hard magnetic material comprising SmCo, hard ferrite orNdFeB.
 8. The magnetoresistive device according to claim 1, wherein themagnetic layer comprises a soft magnetic layer, and wherein the softmagnetic layer comprises a soft magnetic material exchange biased by anatural antiferromagnet.
 9. The magnetoresistive device according toclaim 1, wherein the hard magnetic layer has a magnetization, athickness and a vertical distance from the xMR-sensor such that thestrength of the bias magnetic field generated along the easy axis of thexMR-sensor is between 2 mT and 10 mT.
 10. The magnetoresistive deviceaccording to claim 1, wherein the insulating layer comprises adielectric layer deposited on the carrier.
 11. The magnetoresistivedevice according to claim 10, wherein the dielectric layer is depositedon the carrier with a thickness between 3 μm and 10 μm.